1. Field of the Invention
This invention is related to milling and drilling methods, tools and whipstocks; and in one aspect to single-trip milling methods and systems.
2. Description of Related Art
Milling tools are used to cut out windows or pockets from a tubular, e.g. for directional drilling and sidetracking; and to remove materials downhole in a well bore, such as pipe, casing, casing liners, tubing, or jammed tools. Drilling systems are used to drill wellbores, both main boreholes and lateral bores extending therefrom. The prior art discloses various types of drilling, milling and cutting tools provided for drilling a formation or for cutting or milling existing pipe or casing previously installed in a well. Certain of these tools have cutting blades or surfaces and are lowered into the well or casing and then rotated in a drilling or cutting operation. With certain tools, a suitable drilling fluid is pumped down a central bore of a tool for discharge beneath the cutting blades. An upward flow of the discharged fluid in the annulus outside the tool removes from the well cuttings or chips resulting from the cutting operation. Milling of casing can result in the formation of part of a lateral borehole when a mill exits the casing and bores into the formation.
Milling tools have been used for removing a section or "window" of existing casing from a well bore to permit a sidetracking operation in directional drilling, to provide a perforated production zone at a desired level, to provide cement bonding between a small diameter casing and the adjacent formation, or to remove a loose joint of surface pipe. Also, milling tools are used for milling or reaming collapsed casing, for removing burrs or other imperfections from windows in the casing system, for placing whipstocks in directional drilling, or for aiding in correcting dented or mashed-in areas of casing or the like.
Prior art sidetracking methods use cutting tools of the type having cutting blades and use a diverter or a deflector such as a whipstock to cause the tool to be moved laterally while it is being moved downwardly in the well during rotation of the tool to cut an elongated opening, pocket, or window in the well casing.
Certain prior art well sidetracking operations which employ a whipstock also employ a variety of different milling tools used in a certain sequence. This sequence of operation requires a plurality of "trips" into the wellbore. For example, in certain multi-trip operations, a packer is set in a wellbore at a desired location. This packer acts as an anchor against which tools above it may be urged to activate different tool functions. The packer typically has a key or other orientation indicating member. The packer's orientation is checked by running a tool such as a gyroscope indicator into the wellbore. A whipstock-mill combination tool is then run into the wellbore by first properly orienting a stinger at the bottom of the tool with respect to a concave face of the tool's whipstock. Splined connections between a stinger and the tool body facilitate correct stinger orientation. A starting mill is secured at the top of the whipstock, e.g. with a setting stud and nut. The tool is then lowered into the wellbore so that the packer engages the stinger and the tool is oriented. Slips extend from the stinger and engage the side of the wellbore to prevent movement of the tool in the wellbore. Pulling on the tool then shears the setting stud, freeing the starting mill from the tool. Rotation of the string with the starting mill rotates the mill. The starting mill has a tapered portion which is slowly lowered to contact a pilot lug on the concave face of the whipstock. This forces the starting mill into the casing to mill off the pilot lug and cut an initial window in the casing. The starting mill is then removed from the wellbore. A window mill, e.g. on a flexible joint of drill pipe, is lowered into the wellbore and rotated to mill down from the initial window formed by the starting mill. Typically then a window mill with a watermelon mill mills all the way down the concave face of the whipstock forming a desired cut-out window in the casing. This may take multiple trips. Then, the used window mill is removed and a new window mill and string mill and a watermelon mill are run into the wellbore with a drill collar (for rigidity) on top of the watermelon mill to lengthen and straighten out the window and smooth out the window-casing-open-hole transition area. The tool is then removed from the wellbore.
There has long been a need for an efficient and effective milling method in which the number of trips into the wellbore is reduced. There has long been a need for tools useful in such methods, particularly in single-trip milling methods.